1. Field of the Invention
The present invention relates generally to joining sheet metal or other sheet materials, and more particularly to a method and apparatus for forming such joints.
2. Description of the Prior Art
There are various apparatus and methods in the art for joining a plurality of pieces of sheet metal by punching or otherwise manipulating them to cause them to be deformed into an interlocking relationship in a predetermined area. For example, U.S. Pat. No. 4,459,735 discloses a method for joining a plurality of pieces of sheet metal by first drawing and then laterally extruding the sheet material to be joined in an enlarged shape which will permanently and mechanically interlock the two sheets of metal. The apparatus for achieving such interlocking of the metal sheets consists of a punch assembly and a die assembly, the punch assembly having a punch which enters into a cavity in a die body having a bottom communicating with a circularly and laterally extending groove for accepting the extruded matter from the two metal sheets. Since it would have been impossible for withdrawing the two metal sheets from the die body because of the circular and lateral extruded metal, the die body is provided with movable segments which retract diametrically apart to release the extruded ring formed by the groove in the die body. The known apparatus is relatively complex in design and requires power actuation of both the punch and the portions of the die, thereby increasing the cost of the equipment as well as the energy required for the punching operation.